The object of the invention is a method and a device for testing differential protective relays and systems. Differential protective relays and systems of such a type are used as protective equipment for the monitoring of the widest possible variety of electrical equipment used in power engineering. Electrical equipment of this type can include, for example, a high-voltage or medium-voltage transformer, a bus bar, a generator, a line or a cable, and other similar kinds of electrical equipment. For safety reasons, these types of electrical equipment used in power engineering are provided with differential protective relays which have the job of disconnecting the electrical equipment to be protected from the power supply network in the event of a fault.
The object of the present invention is a method and a device for testing such differential protective relays and differential protective systems, with the goal of safeguarding the function of such differential protective relays and differential protective systems (guaranteeing their protective function).
In conjunction with that, the function testing of the differential protective relay must be possible with installation-specific parameterizations and settings.
By using the test method that is being introduced, it is possible to verify the correctness of the installation-specific design, parameterization and settings, and wiring of the differential protective relay or differential protective system, as well as its protective function.
A further object of the invention is the replacement and improvement of the primary test methods which have previously been carried out, e.g., the 380-volt method, which, due to the small test values, permit only limited and often unclear information.
The designation differential protective system includes the matching converter circuit, particularly with the use of conventional differential protective equipment.
At the present time, numerical differential protective equipment with software-implemented switch assembly matching and zero current elimination are being tested almost exclusively by means of a single-sided current feed at a single point in the characteristic region, which does not permit reliable information concerning the functional capability of the differential protective relay. A few large utilities are testing differential protective relays by means of a double-sided current feed with two controllable current sources, whereby the current vector calculation and the test wiring is difficult and requires specialized knowledge, and is limited to a single-pole and double-pole fault simulation. Finally, the latter utilities do special testing of the correctness of the design, parameterization and setting, and wiring of the differential protective system on transformers by means of a three-phase primary test method (380-volt method). Tests in the characteristic region are also carried out by manufacturers of protective equipment by using two current generators and parameterized switch assembly Yy0 and Yy6.
Such known test methods can, for example, be found in the xe2x80x9cIEEE Guide for Differential and Polarizing Relay Circuit Testingxe2x80x9d, IEEE C37.103-1990, ISBN 1-55937-058-0, pages 21 ff.
The known test instructions show that testing is being done with the simplest of equipment. As a rule, several formulas and current tables are shown for a simple testing of the relay. The testing is usually carried out with single-sided current feed. On occasion, a second current generator is used in order to be able to adjust the stabilization current independently of the differential current.
A complete check of the relay and the protective systems without rewiring is completely impossible, as is the testing of the entire stabilization characteristic curve. It is not always possible to carry out the known 380-volt test due to conditions at the site, and the test currents that are available are often too small to be able to provide meaningful results.
It is therefore the task of the present invention to further development a method and a device of the type mentioned at the beginning, so that all of the parameters relevant to the protective function of a differential protective relay or system can be tested in a simple and exact way, and thus a complete test is possible.
To perform the required task, the invention is characterized by the features of claim 1.
A test method is suggested which provides for a three-phase circuit for connecting a three-phase current system to the primary, secondary and, if applicable, tertiary side (6-9 current generators), plus, if applicable, the additional connecting of separate zero currents.
The item under test is connected once, and can then be tested in its complete functionality. The checking is not carried by means of any kind of current values that are calculated manually or read from a table, instead, it is carried out directly in the transformed level of the stabilization characteristic curve IDIFF/ISTAB (operating characteristic IDIFF/IBIAS) and/or the matched (virtual) currents IS=f(IP). The calculation of the current vectors is carried out automatically, taking into consideration the electrical equipment to be protected, the current converter ratios, the fault type and the fault location.
With this new test method, possibilities are provided for the testing of differential protective systems with respect to function and to the object being tested. The method allows the testing of the special parameters of line-differential protective devices and bus-bar protective devices, as well as of transformer, generator and motor differential protective devices which process the measured value xe2x80x9ccurrentxe2x80x9d of all of the electrically connected protected objects with regard to their current differential or phase angle difference. The complexity of the protected object nodal point is limited to three legs.
The foundation of all stationary test methods is the model of a transformer with three windings. The other protected objects can also be simulated by means of this model through the selection of specific parameters. The allocation of the voltage levels remains fixed. The left winding with feed possibility is always used as the primary side (P). The right winding with feed possibility is always used as the secondary side (S). The tertiary side (T) can be used as pure fault or load side only with a three-winding device or a three-leg device (bus bar).
It is an essential feature of the invention that the protected object is simulated by means of software so that it is simulated with its most important parameters. This simulation of the protected object takes place in the test facility itself The currents calculated in the simulation are then output to the connected differential protective relay or system.
For the test in this case, the test facility with 6 to 9 current generators instead of the current converter is connected directly to the protective relay or system that is to be tested. A simulation of the transformer behavior is carried out in the test facility, and the calculated current vectors are fed into the protective relay or system that is to be tested:
A method for testing the switch assembly matching and the correction of the value will now be explained in the following.
In the case of the transformer, the test currents of the individual windings are dependent upon the effective switch assembly and the numerical index of the switch assembly, and differ in their phase positions. With star or delta transformers, the use of stepping switches, or because of differing INConverter/INTransformer ratios of the windings to be compared, the values of the test currents are also different. The current comparison must thus be traced back to the currents flowing in the individual branches or to a reference winding.
The correct calculation of the currents to be compared from the measured secondary line currents is verified by the test method described here. In addition, a check is carried out with regard to the correct parameterization of the protective device and the correct design and implementation of the protective system, along with the device function with respect to the matching of the measured values. The correct protection device function is tested with identical parameterization of the protection device and the test environment.
In the present description, the ideal protected object is simulated with no consideration of the effects of the voltage regulation, copper and iron losses, or charging currents.
The basis for the vector calculation is the model of a three-winding transformer with switchable feed side. For flow-through faults, the feed can be from one side only. The primary or secondary winding can be selected as the feed side. The feed side is automatically switched after a fault location has been selected. For example, fault on the P side= greater than feed on the S side.
The standard fault types 1-pole, 2-pole, 3-pole plus the 3-pole operating state are realized as flow-through currents in the manual mode within the range O-INTransformer 100%/Uk. In the case of a three-winding transformer, a three-phase load state can be selected on one winding, while in addition a fault case can be selected on the given other one. As a result, the item under test is subjected to measurement values on all ends simultaneously. The test values of the feed side are calculated from the test values of the load or fault side by means of the transformer model mentioned.
In the following, a method for the testing of the trip characteristic curve IDIFT=f(ISTAB) is described.
The detection of a fault in the protection range does not depend solely on the size of a flowing differential current IDIFF=|IP-IS|. During the operating state and when there are external faults, differential currents occur, the causes for which can be found in
the magnetization current
influence of the step switch
ratio error of the converter and which may provide an incorrect image of the state of the protected object. For that reason, it is important to use a suitable stabilizing value Ibias≈|IP|+|IS| (or similar definitions). The continuously described values IP and IS are virtual values which are not immediately apparent from the calculation model, and which are used as input values for the calculation in the Diff/Stab level in the protective device. They are the starting point for the calculation of the test values.
The checking of the described function must be possible with a protective device parameterized in an installation-specific way, and it is used as a verification of the parameterized trip characteristic curve. In conjunction with that, it should be possible for the trip characteristic curve to be recorded through evaluation of the off command by means of binary input standard fault types. This means that the function is based on testing that is multi-sided and, depending on the particular fault type, multi-pole.
The testing is carried out with concrete fault conditions (e.g., 2-pole fault on the secondary side) which are brought into this function by means of the symbol for the protected object in accordance with the calculation model.
The testing is carried out automatically or manually in the DIFF-STAB level (see test environment).
It should be possible to select between two methods. The necessary differential current is generated by means of a pure difference in magnitude of the currents to be compared, IP, IS.
For the single-pole fault, a parameter is to be provided which takes into consideration the treatment of the zero system in the protective device. If the protective device works with its own zero current measurement, no special conditions have to be taken into consideration. If the calculated zero current is calculated from the measured line currents, then the IP, IS calculated from the selected DIFF and STAB values must be internally multiplied by the factor 3/2.
Based upon the comments above, the invention has the following advantages over the state of the art:
No rewiring is needed for conductor-selective testing with various types of faults.
Complicated manual calculation of the required current vectors is not necessary.
Testability of transformer differential protective equipment with all switch assemblies and three-pole faults.
Coordinated output of up to 9 (or 11) test currents.
Testing of the protective device parameterization of numerical relays and the design and implementation of conventional differential protection systems through protected object simulation under substantially better measurement conditions than with the comparable 380-volt method.
Replacement of the 380-volt method, and its disadvantage of the limited test current size resulting from a combination of existing test methods, with the method described here.
The test method allows working directly within the characteristic region of the trip characteristic (operating characteristic).
Method for checking the stabilization behavior of differential protective equipment under any desired normal operating states as well as under external faults.
The essential features of the present invention thus lie in the following technical science:
Test method in which a 3-phase connecting of the test currents is made to each leg or winding (e.g., primary, secondary, tertiary feed in the case of a 3-winding transformer protective relay) of the arrangement to be tested, as well as the optional connection of separate zero currents. A test is thus carried out with 6 to 9 (or 11) current generators.
Test method of differential protective equipment in which the specification of the test values in the transformed levels of the trip characteristic curve is carried out in the form of Idiff and Istab values, and which, by means of a test facility, automatically applies the appropriate current values to the inputs of the equipment to be tested (digital protective relay or conventional protective relay including matching converter) for all simple fault types, while taking into consideration the selected piece of equipment to be protected (line, bus bar, transformer, generator, unit) and its parameters (switch assembly, converter ratio relationships, star point grounding, etc.).
Function-related and protected object-related testing of differential protective devices and systems, and replacement or improvement of the previously used 380-volt method.
The method is used for the testing of the magnitude correction and switch assembly correction, as well as zero-current elimination, particularly during startup.
From the presentation above, it is thus clear that the core of the present invention lies in the fact that now, for the first time, a function-related as well as protected object-related testing of differential protective systems, particularly of differential protective relays can be carried out. That was not possible in the state of the art.
The testing 6f the trip characteristic is carried out by means of two-sided current feed (primary and secondary or primary and tertiary). In the case of three windings, the secondary or the tertiary can be selected.
Fundamentally, a distinction must be made as to which values are used for the calculation of the value pair IDIFF and ISTAB in the protective device.
The calculation of the value pair IDIFF and ISTAB is carried out in the branch of the reference winding. The currents IP, IS, IT which are used for the calculation are identical to the branch currents lPS, ISS, ITS of the reference winding.
With most of the relay manufacturers (Siemens, AEG, ABB), the calculation of the value pair IDIFF and ISTAB is carried out in the conductors of a reference side. The reference side can be adjusted within the test environment, the primary winding (winding 1 in the protective device) is to be selected as the default.
Differential relays work conductor-selectively. In order to have a reasonable distribution of current in the individual phases, the relative angle and magnitude relationships in the case of an external fault are used as the basis for the calculation. If the reference winding is defined as the fault side, the current share corresponds to the fault current vector IF. For a fault on the side opposite the reference point, the resulting current share of the reference side must be calculated. This current share in the individual phases, which results from the selected fault type IF and switch assembly SGx, is to be calculated on the fault side by determining the current matrix M by means of the model before each test, using a different switch assembly and fault type. In the so-called matrix M, the relative magnitude and the vectorial position of the phases is to be stored qualitatively. In contrast to the method described further above, for this test method the occupied coefficients of the fault current vectors IF are not always one.
Problem: Since with a two-pole fault on the triangle side, there are two currents on the star side with half the magnitude of the third, the characteristic curve is tested at two points simultaneously. Both value pairs have the same rise. Depending on the location in the Diff/Stab level, normalization must be made to the minimum or the maximum line current.
The inventive object of the present invention arises not just from the object of the individual patent claims, but also from the combining of the individual patent claims with each other.
All of the information and features contained in the documentation, including the abstract, in particular, the spatial configuration represented in the drawings, are claimed as being essential to the invention, to the extent that they are new with respect to the state of the art either individually or in combination.